Femoral acetabular impingement (FAI) is a condition affecting the ball and socket of a hip joint and surrounding soft tissues. Because FAI can lead to painful cartilage injuries, labral tears, and arthritis, methods of treatment or prevention are highly desirable.
FAI occurs when the femoral head rubs abnormally against or within the acetabular socket. Two principle types of FAI are recognized. Cam impingement occurs when one or more cam lesions on the femoral neck impinge on the acetabular rim during motion of the hip. Pincer impingement occurs when one or more pincer lesions on the acetabular rim produce an overcoverage of the acetabulum which repeatedly hits the femoral neck during motion of the hip. In many cases, both cam and pincer impingement are present.
Three primary motion types determine the orientation of the femoral neck to the acetabular rim and consequently affect the degree of femoral acetabular impingement experienced by a person during physical activity. As shown in FIG. 1A, these motions types are flexion 101, internal rotation 102, and adduction 103. Flexion 101 refers to the degree to which the leg is raised by the hip 111. Internal rotation 102 refers to the rotation of the thigh 112 toward the sagittal plane and the opposite thigh 122. Adduction refers to the lateral translation of the knee 113 toward the sagittal plane and the opposite knee 123. Any of these motions independently or the combination of these three movements occurring together can result in the femoral head contacting the acetabular rim at an anterior (either inward or outward) portion of the rim. Repeated contact can cause breakdown of the soft tissues and result in symptomatic femoral acetabular impingement.